18" or 24" diameter risers?

[BigKielbasa]

Hi, i have an old septic vault approx. 6ft underground. It has 2 concrete lids that measure approx. 58" wide and 60" long. I fixed a
broken pipe from roots entering. Now i want to put risers on the lids. I know i can do this but not sure what diameter size to use, 18" or 24"?
Why would one be used over the other?

 

[Pipe Dreams]

24 inch is what you want, Sewer lids AKA rings are made to sit on 24 inch concrete pipe. The cast iron ring is about 500$

 

[BigKielbasa]

24 inch is what you want, Sewer lids AKA rings are made to sit on 24 inch concrete pipe. The cast iron ring is about 500$

why 24" opposed to 18"? cast iron ring? I see they make plastic adapter rings for the corrugated pipe. What are you referring to?

 

[Twowaxhack]

why 24" opposed to 18"? cast iron ring? I see they make plastic adapter rings for the corrugated pipe. What are you referring to?

Despite what you’ve been told, Bigger is better.

 

[Pipe Dreams]

why 24" opposed to 18"? cast iron ring? I see they make plastic adapter rings for the corrugated pipe. What are you referring to?

I may have misunderstood, but if you are referring to a concrete septic tank, or "interceptor" typically risers are 24 inch concrete pipe topped with a manhole cover made of cast iron. The covers are 24" not 18"...........the ring and cover is a manhole cover like what you see in the middle of the street.

If your tank is corrugated or you are using corrugated pipe as a riser, then fine , no problem. The riser is really only for observation and service, be sure no to drive over them or near them with a heay wehicle